1. Field of the Invention
The invention relates to a cooling apparatus for a dot matrix impact print head of the kind used in dot matrix serial printers.
2. Description of the Prior Art
It is known that in dot matrix serial printers a printing head slidably mounted on guide bars is moved along a print line in front of and transverse to a print support to perform printing thereon. The print head includes a set of printing needles or equivalent elements, which are energized by a corresponding set of electromagnets, to transfer, by impact pressure, the pigment of an inked ribbon to the printing support. In spite of the several improvements which have been adopted in the art to increase the efficiency of electromagnets, most of the electrical power supplied to the electromagnetic actuators, is not converted to printing work, but it is wasted in hysteresis losses within the magnetic materials forming the electromagnet cores and in resistive losses within the electromagnet coils. These losses develop heat which must be dissipated. Heat dissipation is usually obtained by thermal exchange with the air surrounding the print head because of the difference in temperature which arises between the print head body and the surrounding air. To improve the thermal exchange and to limit the thermal step between air and print head, cooling elements are often used which increase the thermal exchange surface by means of finger or wing shaped portions. The print head movement is further utilized to increase the thermal transfer, and in some cases air flow is further induced by fans.
In spite of these expedients, print head overheating is often a problem especially in case of high speed printing heads. This problem has not been completely overcome. Thus in order to prevent print head damage, thermal sensors are used, which senses the temperature in the printing head and which inhibit its further operation when a preestablished temperature ceiling is reached. The heating problem becomes further crucial in those printers where, in order to reduce the noise caused by the electromagnet, the operation of the whole print head is enclosed in a noise deadening material which greatly reduces the thermal conductivity of the print head body and substantially causes the thermal isolation of the print head. Some form of indirect cooling may overcome such problem. For instance, liquid cooling is much more efficient than air cooling; but to be effective a complex and relatively expensive apparatus is required, involving the use of a pump, and heat radiators. As far as is known, no attempts have been made in this direction. The invention, as claimed, is intended to remedy these drawbacks.